1. Field of the Invention
The present invention relates to a sheet post-processing apparatus and an image forming apparatus.
2. Description of the Related Art
In image forming apparatuses such as a laser printer and a color image copying machine using the electrophotographic process, in general, the following method is adopted. Image data input from a personal computer or an image input device is exposed by a laser or the like to form an electrostatic latent image on an image carrier such as a photosensitive drum. Toner is developed by a developing device and then transferred to a sheet such as a form. The toner is then fused onto the sheet by a fixing unit of the heating roller type or the like to fix an image, and the sheet is discharged.
Image forming apparatuses aiming at automation of operations are also provided. These apparatuses are connected with a post-processing apparatus for performing post-processing including stapling, punching, sorting (gathering), bookbinding, and folding. Sheet post-processing by the post-processing apparatus includes stacking processing for sorting sheets for every copy and stacking them on a discharge tray and stapling processing for stapling post-processed sheets for every predetermined number of sheets and stacking them on a stack tray.
As an image forming apparatus equipped with a post-processing apparatus, an image forming apparatus disclosed in Japanese Patent No. 4199203 is known for example. The image forming apparatus includes a document scanning unit arranged at the top of the apparatus body, a paper feeding unit arranged at the bottom of the apparatus body, a printing unit arranged in between the document scanning unit and the paper feeding unit, a sheet post-processing unit that can perform a plurality pieces of sheet post-processing on sheets that are conveyed from the apparatus body after being printed by the printing unit, and a discharging unit to which the sheets after post-processing are discharged, both units arranged in a space within the apparatus body.
In the image forming apparatus disclosed in Japanese Patent No. 4199203, however, when sheets are conveyed from the apparatus body through the short edge feed (SEF), post processing can be performed on the short edge side that orthogonal to the sheet conveying direction, but not on the long edge side that is parallel to the sheet conveying direction. There is also a problem that, because a punching unit and a staple unit in the sheet post-processing unit are collaterally arranged in the horizontal direction, the apparatus body has a large lateral size.
Therefore, there is a need to provide a sheet post-processing apparatus that can incorporate a plurality pieces of post-processing units for performing post-processing on sheets in a space-saving manner, switch the sheet conveying direction smoothly, and perform post-processing on sheets without degrading productivity and to provide an image forming apparatus including the post-processing apparatus.